The present invention relates to apparatus for making holes in sheet material, especially for making holes in cigarette paper, imitation cork or like wrapping material for plain or filter tipped cigarettes, cigars or cigarillos and/or in wrapping material for filter mouthpieces which are combined or about to be combined with plain cigarettes, cigars or cigarillos to form filter tipped cigarettes, cigarillos or cigars. For the sake of simplicity, the invention will be described with reference to the making of perforations or holes in wrapping material for filter tipped cigarettes with the understanding, however, that the same apparatus can be used with equal advantage to make holes in wrappers of plain cigarettes or plain or filter tipped cigars or cigarillos or in the wrappers of filter mouthpieces (including simple mouthpieces, composite or multiplex mouthpieces as well as mouthpieces of the type known as recessed filters and mouthpieces for papyrossi or the like).
It is already known to equip a cigarette making or filter tipping machine with an apparatus which perforates the wrapping material to insure that a certain amount of atmospheric air can be admixed to the column of tobacco smoke in order to exert a beneficial influence on the quantity and effects of nicotine and/or condensate. It is also known to equip such apparatus with a source of coherent radiation, particularly a laser, which burns holes into the wrapping material, either prior to draping of such wrapping material around a filler consisting of tobacco and/or filter material or subsequent to draping, i.e., subsequent to severing of the web. For example, it is known to resort to a laser which burns holes into the outer tubular envelope of a filter mouthpiece at the inner end of the tobacco filler of a filter cigarette. At the present time, lasers are used to form a single row of perforations. Several rows of perforations can be formed by the obvious expedient of resorting to two or more lasers, i.e., by using a discrete laser for each row of perforations; however, this contributes excessively to the initial and maintenance cost of such apparatus. On the other hand, the making of two or more rows of perforations in one and the same wrapper is often desirable, for example, to perforate the outer envelope of a filter mouthpiece of double unit length which forms part of a filter cigarette of double unit length. By forming the envelope with two rows of perforations, one insures that a row of perforations is provided in the filter mouthpiece of each of two filter cigarettes of unit length which are obtained by severing a filter cigarette of double unit length midway across the filter mouthpiece. This holds true regardless of whether the perforations are formed in the web of wrapping material which is about to be converted into discrete uniting bands for connecting pairs of plain cigarettes with filter mouthpieces of double unit length or the perforations are formed in the tubular envelope which is obtained by convoluting a uniting band around a filter mouthpiece of double unit length and the adjacent end portions of corresponding plain cigarettes of unit length. Furthermore, it is often desirable to provide the wrapping material with several rows of perforations in order to enhance the appearance of the perforated zone and/or to achieve a more uniform mixing of cool atmospheric air with tobacco smoke.
As mentioned above, the provision of two or more discrete lasers contributes enormously to the initial cost of the machine which produces and/or processes the wrapping material.